Field of the Invention
The present invention relates to a photoelectric encoder used in precision measurement.
Description of the Related Art
Conventionally, a photoelectric encoder (below, sometimes referred to as “encoder”) has been used in precision measurement of the likes of linear displacement or angular displacement. The encoder is mounted in the likes of a three-dimensional measuring instrument or an image measuring instrument. The encoder comprises: a light source; a scale including an optical grid; and a light-receiving unit including a plurality of light-receiving elements and having an index grid on a light-receiving surface, the index grid disposed so as to be movable along with the light source relatively to the scale and configured such that each of the light-receiving elements have phases that differ from each another.
Operation of the encoder is briefly explained. While moving the scale relatively to the light source and the light-receiving unit, light from the light source is irradiated onto the index grid via the optical grid of the scale. This results in generation of a plurality of (for example, four) light-and-dark patterns of sinusoidal light having different phases. These light-and-dark patterns of sinusoidal light represent a light signal. An electrical signal is generated by photoelectric conversion when these light-and-dark patterns of light having different phases are received by the light-receiving elements corresponding to each phase, and this electrical signal is utilized to measure an amount of linear displacement, and so on.
Incidentally, in the case of an encoder having an object of one-dimensional measurement, the plurality of light-receiving elements are generally disposed in a line along a measurement axis (for example, JP 2005-208015 A).
Therefore, in order to increase resolution performance of measurement of the displacement amount, it is naturally desirable to dispose an increased number of light-receiving elements having small width in a measurement axis direction, in the light receiving unit. However, size of the light-receiving element is determined by a manufacturing process of the light-receiving element. In other words, in the case of employing conventional technology, it is difficult to make a detection pitch of the light-and-dark pattern of light smaller than a limit width in the measurement axis direction of the light-receiving element restricted by the manufacturing process of the light-receiving element.
The present invention was made in view of the above-mentioned problem and has an object of providing a photoelectric encoder realizing a higher resolution performance of the light-receiving unit.